This invention relates to a muffle furnace for continuous heat treatment during passage of material therethrough, of products whose production cycle includes a treatment of predetermined duration at elevated temperature. This is the case with certain refractories, carbon-containing products, such as electrodes which are impregnated, after a first firing, with a pyrolyzable and carbonizable carbon-containing material, and also with metals for the purpose of transforming them, and with metal alloys for the purpose of homogenizing them and forming a solid solution with the alloying elements.
In the following, the term "heat treatment" describes any operation in which one of the above products is heated to a high temperature for the purpose of providing it with particular properties.
These heat treatments are often carried out in static electrically heated or flame-heated furnaces. This is the case, for example, with furnaces for reheating metal bilets consisting of various types of steel or aluminum alloys, for example in direct contact with the combustion gases, or furnace chambers for firing carbon electrodes at temperatures of from about 800.degree. to about 1200.degree. C.
These are discontinuous operations which suffer from all the disadvantages associated with these processes: difficulty in controlling the temperature often producing heterogeneous products; prolonged utilization of the furnaces due to the slow speed of the charging and withdrawing operations; and the substantial bulkiness of the equipment. Problems are also caused, in certain cases, by the products to be treated being directly contacted by the combustion gases.